I hardly see how marriage predates laws and predates governments, unless you believe they are made in heaven. In which case, there can be no divorce, because God couldn't make a mistake, could He? (Well, He never married, so He maybe isn't too swift about it). Western marriages until very recently were dependent on church law and ratified by state law. Presumably, unless you were living together and never got officially married (Oh MIGOD!!!) being married for 35 years (in Jimmy's case) was a public act, carried out in front of witnesses, and enshrined in law. If the predating of laws is what counts, then presumably incest, multiple partners, and who knows what all are also valid. Monogamy is not exactly universal (to say the least) in so-called primitive societies "pre-dating law" (although all the so-called primitive societies I know have all kinds of socially sanctioned rules). It is a social artefact, and a nice one, built upon some impulses in human behaviour that are subjected to reinforcing rituals that our society finds valuable.

yours, Peter T.